Recently, as a fuel of a marine diesel engine centered on an ocean-going vessel, a so-called heavy oil C, which is a residual oil appearing in conjunction with an oil refinement, is generally used. The heavy oil which is used in the marine diesel engine in this way is also called a bunker oil.
The ocean-going vessel calls in at ports in countries other than its own country, and carries out a replenishing of fuel in the ports, but as oil refinement methods differ according to the country, a quality of a residual oil which is to be the fuel differs in each country, and there has been a danger of the marine diesel engine being damaged in a case of replenishing with a fuel of an inferior quality.
In particular, with the marine diesel engine, an occurrence of a scuffing has been known as that which causes the most serious damage. The scuffing being a damage, such as a scratching of a cylinder wall, occurring due to a piston and a cylinder sliding in a condition in which there is a lack of a lubricant, in some cases, there has been a danger of it leading to a damage to the marine diesel engine.
Therein, as a method of checking a quality of a replenishing fuel, an inspection apparatus which inspects the quality of the fuel has been proposed by Fuel Tech, Inc. With the inspection apparatus, the fuel being caused to combust in a combustion chamber, and a combustion condition being detected from a pressure change in the combustion chamber at the time of the combustion, in particular, focusing on an ignition lag, which is a time from injecting the fuel into the combustion chamber until the injected fuel ignites, a fuel quality evaluation is carried out.
With Fuel Tech, Inc.'s inspection apparatus, the detection of the combustion condition is carried out based on the pressure change in the combustion chamber, but recently, an evaluation method has been proposed which, directly observing the combustion condition by mounting a heat resistant, transparent glass, such as a quartz glass, on the combustion chamber, providing an observation window, and photographing the combustion condition inside the combustion chamber through the observation window with a high speed camera or the like, evaluates the quality of the fuel from a length of a flame or a length of an after burning time (for example, refer to Patent Document 1).    Patent Document 1: JP-A-2001-329906